Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a familial heterogeneous clinical and molecular disease characterized by dilatation and dysfunction of the right ventricle and ventricular arrhythmias. The ventricular arrhythmias are heart rate and catecholamine dependent. There may also be involvement of the left ventricle. The diagnosis of ARVC is critical because therapy including implantable defibrillators may prevent sudden death. However identification of subjects at risk remains a major challenge due to limitation of imaging and diagnostic techniques. This study is designed to investigate family members at risk for ARVC because of a relative with known ARVC. Studies will include investigation of the utility of a novel diagnostic test, magnetic resonance imaging, and genetic studies. A protocol has been approved by the Institutional Review Board.